ProjectSummary/Abstract Primary aldosteronism (PA) is the most common cause of secondary hypertension, representing a significant risk factor for cardiovascular, cerebrovascular events and chronic kidney disease. PA accounts for up to 24% of all refractory hypertension and its prevalence is estimated to be as high as 1 in 50 people. In normal physiology adrenal aldosterone production is tightly regulated by angiotensin II and potassium levels. In PA aldosterone, at least in part, escapes these regulatory mechanisms. 35% of PA are caused by unilateral adenomas and recent research has focused on somatic mutations causing aldosterone production in these tumors, including mutations in a potassium channel (KCNJ5), Na-K ATPase (ATP1A1), Ca ATPase (ATP2B3) and calcium channel (CACNA1D). Mutations in these genes are believed to induce membrane depolarization and increase in calcium influx leading to increased CYP11B2 transcription and ultimately aldosterone production. The majority (65%) of PA is caused by idiopathic hyperaldosteonism (IHA), with both both adrenal glands being the source of aldosterone. Germline mutations (e.g. CYP11B2/CYP11B1 cross-over, KCNJ5, CACNA1D) explain less than ~2% of all IHA cases. The current proposal aims to define additional constitutional genetic mutations as causes for IHA. In preliminary analyses we have identified several mutations in candidate genes, particularly membrane localized ion channels and ATPases. The hypothesis is that dominantly inherited mutations can cause IHA or at least serve as a risk factor for the disease. Aim 1 is designed to functionally characterize the effect of the mutations on electrophysiology, intracellular signaling and aldosterone production in adrenocortical cells. Aim 2 will explore the role of the candidate genes in apparently sporadic cases of IHA by targeted gene sequencing. Aim 3 will explore the role of the described mutations as a somatic event causing development of adenomas. The results of this study will lead to improvement of our understanding of the adrenal pathophysiology that underlies PA, improve the diagnosis of PA and will open new routes of a targeted therapy of PA in the future.